The successful storage of medical solutions in containers is dependent upon a variety of factors all relying on the type of material chosen for the packaging. In order to qualify for the use in pharmaceutical packaging the material must possess good barrier and leaking properties. The material must have a high barrier against preservatives from the medical solution and at the same time liberate as few leakage substances to the medical solution as possible.
In the prior art such material has been described as bromobutyl (halogenated butyl rubber). EP 841 374 discloses a moulded bromobutyl rubber part suitable for being in contact with medical solutions. The rubber part is moulded by the means of vulcanisation and contains a fine powder of ultra-high-molecular-weight polyethylene.
An important aspect in the research field of pharmaceutical packaging is to continuously improve the materials for holding pharmaceuticals. The emphasis of this research is particularly relevant in relation to obtaining satisfactory leakage properties. Another and more appropriate material for the above purpose is described in EP 215 551 as a mixture of bromobutyl and polypropylene (PP). EP 215 551 discloses a high temperature creep resistant thermoplastic elastomer composition for the use in rubber parts, such as stoppers for syringes. The composition comprises vulcanised ethylene-propylene-diene terpolymers and polypropylene with butyl based rubber, the latter being present in small amounts with respect to the polypropylene.
For the purpose of manufacturing medical containers injection-mouldable compositions have proved to be advantageous. U.S. Pat. No. 444,330 discloses a stopper for a medical container made from an injection-mouldable polymeric material containing a blend of a butyl-based rubber, a thermoplastic elastomer and a mouldability improving olefin-based polymer.
It is the object of the present invention to provide a stopper material suitable for use in pharmaceutical packaging having reduced leakage.